There are two types of spoilers you can post. One is a clickable box which lets you specify a title for the spoiler:
[*:3zrsid41]AJK eats children!
[*:3zrsid41]It is scary!
You can insert it either by typing [s poiler= ] (without the space between the S and P), inserting your content and a title after the equals sign and closing off with a [ /s poiler] (again without the space) tag or by clicking the Spoiler button on the create topic/add reply form and doing the same.
It can cover whole paragraphs, lists and so on.
The other type is an inline spoiler. It looks like
Spoilerand you can get it by typing [s poiler] your spoiler and [/ s poiler] to close the tag.